1. Field of the Invention
The present invention relates to an electronic (e.g. a molecular electronic) device including a self-assembled monolayer as the active material and, in particular, an electronic device having a self-assembled monolayer disposed adjacent to a conductive (e.g., metallic) substrate.
2. Description of the Related Art
Organic thin-film transistors (OTFTs) have continued to receive considerable attention as alternatives to traditional inorganic semiconductor transistors based on amorphous silicon channels. The structure of both commonly investigated bottom contact and top contact geometry OTFTs are shown in FIGS. 1B–1D. Progress in the preparation and fabrication of organic semiconductor materials and devices has enhanced the field-effect mobility of OTFTs to ˜1 cm2/V-sec, approaching the limit expected from the values found in single crystal organic solids.
In organic thin-films and crystals, the molecules or oligomers are held together by weak Van der Waals forces such that the π-orbitals on neighboring molecules overlap giving rise to charge transport in the solid state. Charge transport is, however, limited in organic solids by the weak intermolecular binding, giving rise to narrow valence and conduction bands, and by electron-phonon coupling.
Recently there has been research on fabricating OTFTs with narrow channels and also in replacing the commonly used gate insulating inorganic oxide or polymeric thin-films with an insulating, self-assembled monolayer (SAM) such as long chain, alkyltrichlorosilanes (J. Collet et al., “Nano-Field Effect Transistor with an Organic Self-Assembled Monolayer as Gate Insulator”, Applied Physics Letters, Vol. 73, No. 18, Nov. 2, 1998; J. Collet et al., “Low-Voltage, 30 nm Channel Length, Organic Transistors with a Self-Assembled Monolayer as Gate Insulating Films”, Applied Physics Letters, Vol. 76, No. 14, Apr. 3, 2000).
On the other hand, conjugated SAMs have received particular interest as active layers in molecular electronic and photonic devices. The conjugated SAMs that have been investigated are typically short (e.g., less than 4 nm) conjugated molecules. A molecule may also contain other groups or functionalities; the conjugated molecule being one segment of a larger molecule.
Molecular electronic and memory devices are based on intramolecular charge transport and building the desired functionality, such as switching, within the molecule. A molecular scale transistor is an important component for logic applications and has often been referred to as the “holy grail” of molecular electronics.
However, it is desired to improve the performance of conventional molecular devices. Specifically, it is desired to provide an electronic device having a molecular layer (e.g., self-assembled monolayer) with improved electrical properties.